The present invention relates, in general, to a molding apparatus, and especially, but not exclusively, to a molding apparatus for the manufacture of plastic panes, for example, window panes for passenger cars.
Molding apparatuses, involved here, include a core and a female mold member as well as circumferential peripheral dies, with the peripheral dies being attached to the core for movement in closing direction. The core is completely surrounded by the peripheral dies, with the female mold member so configured in the region of the impact areas of the peripheral dies as to complement these impact areas.
FIG. 1 shows a cross sectional illustration of a conventional molding apparatus of this type which includes a fixed mold clamping pate having attached thereon the female mold member and a movable mold clamping plate having attached thereon the core via a core plate. Upon movement of the movable clamping plate toward the fixed clamping plate, the core descends into the female mold member, whereby the movement of the core is guided by the circumferential peripheral dies which also realize a sealing of the cavity defined between the core and the female member. This conventional molding apparatus suffers the drawbacks that the descending peripheral dies are damaged on both mold halves (injection side and closing side) as a result of:
an imprecise centered descent of the core side into the female mold member; PA0 too narrow dimensions of the female mold member as a consequence of mold shrinkage caused by temperature decrease below the very narrow temperature tolerances; PA0 one-sided contact of the descending dies as a consequence of a floating effect which is encountered during compression injection molding and cannot be offset by greater machine tolerances; PA0 excessive core dimension as a consequence of a mold dilatation caused by temperature deviation above the very narrow temperature tolerances.
Attempts were made to address these drawbacks by providing the core with one or more circumferential peripheral dies which are mounted to the core and movable in closing direction and which are able to bear upon flat areas of the female mold member in closed state. An example of such a mold is described in U.S. Pat. No. 4,707,321 for making optical data carriers. The mold has a circular core which is circumscribed by a circular peripheral die which can be moved by compressed air along the core in direction of the female mold member. The peripheral die is hereby formed in one piece in accordance with the diameter of the circular injection molded part. This peripheral die is unsuitable for use with differently designed injection molded parts.
"Patent Abstracts of Japan, Publication Number 08057922 A" discloses a molding apparatus with several peripheral dies which are wrapped around the core and are mounted to the core for movement in closing direction and completely surround the core. Each individual peripheral die is received in a T-shaped groove which is continuous around the entire circumference of the marginal region of the core and open toward the side of the female mold member and which is formed of two pieces in radial direction. In order to realize a close fit of each peripheral die in this groove, without jamming, but yet being shiftable along the core, both halves of each peripheral die are moved apart by spring elements so as to bear upon confronting inside surfaces of the groove. Provided in the bottom of the groove are spring elements by which the peripheral dies are retained in the direction of the female mold member under prestress. When the mold is closed, the peripheral die, jutting out from the groove, is pressed against the female mold member which has a flat configuration in the contact area of the peripheral die. This molding apparatus is complex, and a replacement of defective or worn-off peripheral dies is very cumbersome. A further drawback resides in the fact that the inner part of the peripheral die is pushed outwards when high injection pressures or compression forces are applied, so that plastic mass can escape and/or flashes are encountered on the injection molded part. Although this could conceivably be avoided by sufficiently biasing the bottom spring, this modification would be accompanied by the drawback that the peripheral die can be moved in the T-groove only at great difficulty or can even jam.